Abstract
Upon feeding, mosquito midguts secrete the peritrophic matrix (PM), an extracellular chitin-containing envelope that completely surrounds the blood meal. Because the malaria parasite must cross the PM to complete its life cycle in the mosquito, the PM is a potential barrier for malaria transmission. By antibody screening of an expression library we have identified and partially characterized a cDNA encoding a putative PM protein, termed Anopheles gambiae adult peritrophin 1 (Ag-Aper1). Ag-Aper1 is the first cloned PM gene from a disease vector. Northern analysis detected an abundant Ag-Aper1 transcript only in the adult gut, and not in any other tissues or at any other stages of development. The predicted amino acid sequence indicates that it has two tandem chitin-binding domains that share high sequence similarity with each other and also with the chitin-binding domain of an adult gut-specific chitinase from the same organism. The presumed ability of Ag-Aper1 to bind chitin was verified by a functional assay with the baculovirus-expressed recombinant protein. Ag-Aper1 did bind to chitin but not to cellulose, indicating that Ag-Aper1 binds chitin specifically. The double chitin-binding domain organization of Ag-Aper1 suggests that each protein molecule is able to link two chitin polymer chains. Hence, this protein is likely to act as a molecular linker that connects PM chitin fibrils into a three-dimensional network.
Highlights
The peritrophic matrix (PM)1 is an extracellular layer that surrounds the food bolus in the guts of most arthropods [1,2,3,4]
We report for the first time, the cloning of a PM protein from a disease vector and propose that this PM protein plays a major role in the spatial organization of the PM
If proteins are glycosylated to different extents, the PM protein complexity could be lower than the number of bands in the gel
Summary
The peritrophic matrix (PM) is an extracellular layer that surrounds the food bolus in the guts of most arthropods [1,2,3,4]. The PM may function as a partial barrier to toxins and other macromolecules. It is known that the parasite secretes a chitinase to facilitate the penetration of the PM [12], it is unclear what role, if any, the PM plays in triggering chitinase secretion or whether secretion of other hydrolytic enzymes by the parasite is required. The resolution of these issues will require the elucidation of the molecular composition and structure of the Anopheles PM. We report for the first time, the cloning of a PM protein from a disease vector and propose that this PM protein plays a major role in the spatial organization of the PM
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